Martial arts, tai chi, yoga are all good recommendations. Something where you have to focus on and fix your alignment, and where there is an instructor who will correct you. Dance--yes for a barre type class, maybe to zumba. Zumba is good for balance and coordination, but no one is going to help you fix your posture.
Fixing posture is really hard...I really also like swimming for this. I swim laps for cardio and a little bit of resistance training, and then I spend a lot of time on standing stretches or poses where I am out of alignment on dry land. Being in the water is a tiny bit of support and having less gravity helps thing go in the right place. I do repetitions enough until my proprioception knows it's the right place and can work towards going there out of the water.